The purpose of this project is to prepare suicide substrates (enzyme-activated irreversible inhibitors) for monooxygeneases catalyzing biosynthesis or metabolism of hydroxysterols which may be involved in regulation of cholesterol biosynthesis. The scope of the project comprises design, synthesis, and biological assay of inhibitors of the enzymes mediating 4- and demethylation of lanosterol, 25/26-hydroxylation of cholesterol, and possibly other sterol monooxygenases.